Method for manufacturing a stator core for a dynamoelectric machine

ABSTRACT

A cylindrical laminated body is prepared by winding into a helical shape a continuous first sheet formed by press-punching from a thin first magnetic steel sheet material. A second sheet having a predetermined length is prepared by press-punching from a thicker second magnetic steel sheet material. Next, chamfered portions are formed on edge portions of second recess portions by chamfering the second sheet. Then, the second sheet is bent into an annular shape and the second sheets bent into the annular shape are stacked on both axial ends of the laminated body and integrated by laser welding.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for manufacturing astator core for a dynamoelectric machine such as an automotivealternator, for example, and particularly to a method for manufacturinga stator core formed by laminating a press-formed magnetic steel sheetmaterial.

[0003] 2. Description of the Related Art

[0004]FIG. 8 is a plan explaining a process for forming a laminated bodyby a first sheet in a conventional stator for an automotive alternatordescribed in Japanese Patent Laid-Open No. 2001-112197 (Gazette), forexample, FIG. 9 is a cross section taken along line IX-IX in FIG. 8viewed from the direction of the arrows, FIG. 10 is a plan showing asecond sheet in the conventional stator for an automotive alternator,FIG. 11 is a cross section taken along line XI-XI in FIG. 10 viewed fromthe direction of the arrows, FIG. 12 is an exploded perspective showinga process for inserting conductor segments into a stator core in theconventional stator for an automotive alternator, and FIG. 13 is apartial cross section explaining a mounted state of a stator winding inthe conventional stator for an automotive alternator.

[0005] A conventional stator 1 is constituted by: a cylindrical statorcore 2 in which slots 3 are formed at a predetermined pitch in acircumferential direction so as to open onto an inner circumferentialside; a stator winding 4 installed in the slots 3 of the stator core 2;and insulators 5 mounted inside each of the slots 3.

[0006] The stator core 2 is provided with: a laminated body 7constituted by a first sheet 6; and second sheets 8 disposed at firstand second axial ends of the laminated body 7.

[0007] As shown in FIG. 8, the laminated body 7 is formed into acylindrical shape by winding up the first sheet 6 for a predeterminednumber of winds into a helical shape, the first sheet 6 being formed byusing a press die to punch recess portions 6 a at a predetermined pitchin a strip-shaped magnetic steel sheet material. Here, the recessportions 6 a are superposed in an axial direction of the laminated body7, constituting first slot portions 3 a. In the laminated body 7, thefirst sheet 6 is laminated with the press punch direction aligned, asshown in FIG. 9, and burrs 6 b extending in the press punch directionremain on each layer of the first sheet 6 on inner wall surfaces of thefirst slot portions 3 a.

[0008] As shown in FIG. 10, the second sheets 8 are each formed into anannular shape by using a press die to punch a flat sheet composed of amagnetic steel sheet material having a sheet thickness greater than thatof the first sheet 6. Here, second slot portions 3 b corresponding inposition to the first slot portions 3 a are simultaneously press-formed.As shown in FIG. 11, chamfered portions 8 a are formed on edge portionsof the second slot portions 3 b on a first end side of the second sheets8. Moreover, the second sheets 8 are formed so as to be equal indiameter to the laminated body 7.

[0009] The second sheets 8 are disposed at first and second end surfacesof the laminated body 7 such that the positions of the first slotportions 3 a and the second slot portions 3 b align and the chamferedportions 8 a face away from the laminated body 7, and the stator core 2is prepared by applying several strips of laser welding so as to extendin an axial direction from a first end portion to a second end portionon the outer circumferential surfaces thereof. Moreover, the first andsecond slot portions 3 a and 3 b align in an axial direction,constituting the slots 3.

[0010] As shown in FIGS. 12 and 13, the stator winding 4 is constructedusing a plurality of conductor segments 9 by joining together endportions of the conductor segments 9 by a joining method such aswelding, etc. The conductor segments 9 are each prepared by bending intoa U shape a short length of copper wire having anelectrically-insulating coating. Here, large and small first and secondconductor segments 9 a and 9 b form a basic unit and a plurality ofthese units are used. The conductor segments 9 are housed in the slots 3so as to be surrounded by the insulators 5 such that the insulators 5are interposed between the conductor segments 9 and inner wall surfacesof the slots 3. Together with the electrically-insulating coatingcovering the copper wire of the conductor segments 9, these insulators 5ensure electrical insulation between the conductor segments 9 and thestator core 2.

[0011] The conductor segments 9 and the insulators 5 are inserted intothe slots 3 of the stator core 2 in a direction aligned with the presspunch direction of the first sheet 6, in other words, from top to bottomin FIG. 13. The stator winding 4 is prepared by bending first endportions of the conductor segments 9 extending outward from the slots 3of the stator core 2 as indicated by the arrow in FIG. 13 and joiningthe first end portions to second end portions of conductor segments 9separated by a predetermined pitch.

[0012] In the conventional stator 1 constructed in this manner, becausethe second sheets 8 having a thick sheet thickness are disposed on thefirst and second axial end portions of the laminated body 7, therigidity of the stator core 2 is increased. Thus, the occurrence ofdeformation and peeling of the first sheet 6 having a thin sheetthickness is prevented during insertion of the conductor segments 9.When the stator 1 is fixed by being held from first and second axialends by a frame, the occurrence of warping in outer circumferentialportions of the stator core 2 is reliably prevented. Because therigidity of the stator core 2 is increased, the sheet thickness of thefirst sheet 6 constituting the laminated body 7 can be reduced. Thus,iron loss which is proportional to the square of the sheet thickness ofthe steel sheets is reduced, enabling increased efficiency to beachieved in the dynamoelectric machine.

[0013] Because opening edge portions of the slots 3 at the first andsecond axial end surfaces of the stator core 2 are constituted by thechamfered portions 8 a of the second sheets 8, damage to theelectrically-insulating coating of the conductor segments 9 caused bythe burrs 6 b is avoided during insertion of the conductor segments 9,during bending or joining of the end portions of the conductor segments9, and during shaping of coil ends of the stator winding 4 after joiningof the conductor segments 9, thereby improving electrical insulation.

[0014] In the conventional stator for an automotive alternator, becausethe stator core 2 is prepared, as described above, by preparing thelaminated body 7 by winding the strip-shaped first sheet 6 in which therecess portions 6 a (the first slot portions 3 a) are formed bypress-punching into a helical shape for a predetermined number of winds,preparing the thick annular second sheets 8 in which the second slotportions 3 b are formed by press-punching, forming the chamferedportions 8 a on the edge portions of the second slot portions 3 b of thesecond sheets 8 by chamfering, disposing the faced second sheets 8 atfirst and second ends of the laminated body 7, and integrating thelaminated body 7 and the second sheets 8 by welding, the followingproblems arise, preventing cost reductions:

[0015] First, because the annular second sheets 8 are prepared from aflat magnetic steel sheet material by press-punching, the second sheets8 cannot be prepared from the magnetic steel sheet material efficiently,increasing the amount of magnetic steel sheet material.

[0016] Second, because the chamfered portions 8 a are formed on the edgeportions of the second slot portions 3 b by chamfering the annularsecond sheets 8, slot opening portions are narrow, lowering chamferingprecision, thereby lowering yield.

SUMMARY OF THE INVENTION

[0017] The present invention aims to solve the above problems and anobject of the present invention is to provide a method for manufacturinga stator core for a dynamoelectric machine enabling cost reductions tobe achieved by preparing a second sheet constituting an end plate in astraight shape by press-punching and preparing an annular end plate bybending the straight second sheet to prepare the end plate from amagnetic steel sheet material efficiently and suppress increases inmaterial quantities, and in addition, by forming an chamfered portion onan edge portion of a recess portion by chamfering the straight secondsheet to increase chamfering precision and enable improved yield.

[0018] With the above object in view, according to one aspect of thepresent invention, there is provided a method for manufacturing a statorcore for a dynamoelectric machine, the method including the step ofpreparing a cylindrical laminated body by preparing a continuous firstsheet in which first recess portions are formed at a predeterminedspacing by press-punching from a strip-shaped first magnetic steel sheetmaterial and winding the first sheet into a helical shape such that thefirst recess portions are superposed in an axial direction. Also, themethod includes the step of preparing a second sheet having apredetermined length in which second recess portions are formed at apredetermined spacing by press-punching a second magnetic steel sheetmaterial having a sheet thickness greater than that of the firstmagnetic steel sheet material. Further, the method includes the steps ofbending the second sheet into an annular shape, stacking the secondsheets bent into the annular shape on both axial ends of the laminatedbody such that the second recess portions are superposed on the firstrecess portions in an axial direction, and integrating the laminatedbody and the second sheets stacked together by applying several stripsof welding on an outer circumferential surface of the laminated body andthe second sheets so as to extend from a first end to a second end in anaxial direction.

[0019] Therefore, the method enables the second sheet for an end plateto be prepared from the second magnetic sheet material efficiently,thereby enabling cost reduction to be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a perspective showing a stator for an automotivealternator using a stator core manufactured by a method formanufacturing a stator core according to Embodiment 1 of the presentinvention;

[0021]FIG. 2 is a perspective showing the stator core manufactured bythe method for manufacturing a stator core according to Embodiment 1 ofthe present invention;

[0022]FIG. 3 is a cross section taken along line III-III in FIG. 2viewed from the direction of the arrows;

[0023]FIG. 4 is a perspective explaining the method for manufacturing astator core according to Embodiment 1 of the present invention;

[0024]FIG. 5 is a perspective explaining the method for manufacturingthe stator core manufactured by the method for manufacturing a statorcore according to Embodiment 1 of the present invention;

[0025]FIG. 6 is a perspective explaining the method for manufacturingthe stator core manufactured by the method for manufacturing a statorcore according to Embodiment 1 of the present invention;

[0026]FIG. 7 is a perspective showing a stator core manufactured by amethod for manufacturing a stator core according to Embodiment 2 of thepresent invention;

[0027]FIG. 8 is a plan explaining a process for forming a laminated bodyby a first sheet in a conventional stator for an automotive alternator;

[0028]FIG. 9 is a cross section taken along line IX-IX in FIG. 8 viewedfrom the direction of the arrows;

[0029]FIG. 10 is a plan showing a second sheet in the conventionalstator for an automotive alternator;

[0030]FIG. 11 is a cross section taken along line XI-XI in FIG. 10viewed from the direction of the arrows;

[0031]FIG. 12 is an exploded perspective showing a process for insertingconductor segments into a stator core in the conventional stator for anautomotive alternator; and

[0032]FIG. 13 is a partial cross section explaining a mounted state of astator winding in the conventional stator for an automotive alternator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Preferred embodiments of the present invention will now beexplained with reference to the drawings.

[0034] Embodiment 1

[0035]FIG. 1 is a perspective showing a stator for an automotivealternator using a stator core manufactured by a method formanufacturing a stator core according to Embodiment 1 of the presentinvention, FIG. 2 is a perspective showing the stator core manufacturedby the method for manufacturing a stator core according to Embodiment 1of the present invention, FIG. 3 is a cross section taken along lineIII-III in FIG. 2 viewed from the direction of the arrows, and FIGS. 4to 6 are perspectives explaining the method for manufacturing a statorcore according to Embodiment 1 of the present invention.

[0036] In FIGS. 1 to 3, a stator 10 is constituted by: a cylindricalstator core 11 in which slots 12 are formed at a predetermined pitch ina circumferential direction so as to open onto an inner circumferentialside; and a stator winding 13 installed in the slots 12 of the statorcore 11.

[0037] The stator core 11 is constructed by laminating a pair of endplates 17 composed of a magnetic steel sheet onto first and second axialends of a laminated body 16 formed by laminating a magnetic steel sheetmaterial and integrating by laser welding, for example.

[0038] The stator winding 13 is prepared by mounting three winding phaseportions 15 into groups of the slots 12 so as to be offset by one sloteach, each winding phase portion 15 being formed by installing oneconductor wire 14 composed of a copper wire coated with an electricalinsulator into a wave winding in every third slot 12. Each of thewinding phase portions 15 is formed by preparing an annular unit bywinding one conductor wire 14 for a predetermined number of winds,preparing a star-shaped unit by shaping the annular unit into a starshape, and mounting the star-shaped unit into the slots 12 of the statorcore 11.

[0039] Next, a method for manufacturing the stator core 11 will beexplained.

[0040] First, a single-strip first sheet 20 in which first recessportions 20 a are formed at a predetermined pitch is prepared bypress-forming a hoop material composed of a first magnetic steel sheetmaterial having a thickness of 0.50 mm, for example, using a press die.Then, as shown in FIG. 4, the cylindrical laminated body 16 is preparedby winding the first sheet 20 into a helical shape for a predeterminednumber of winds. At this time, the first recess portions 20 a aresuperposed in an axial direction of the laminated body 16 to constitutethe slots 16 a.

[0041] Second sheets 21 having a predetermined length in which secondrecess portions 21 a are formed at a predetermined pitch are eachprepared by press-forming a flat plate composed of a second magneticsteel sheet material having a thickness of 1.00 mm, for example, using apress die. Here, the length of the second sheets 21 is equivalent to thecircumferential length of the stator core 11. Next, as shown in FIG. 5,these straight second sheets 21 are faced using a press die to formchamfered portions 21 b on edge portions of the second recess portions21 a on a first surface side of each of the second sheets 21. Then, thesecond sheets 21 formed with the chamfered portions 21 b are each bentinto an annular shape. In addition, annular end plates 17 are preparedby abutting first and second end surfaces of the second sheets 21 andjoining the abutted portions 21 c by tungsten inert-gas (TIG) welding.

[0042] Next, the pair of end plates 17, as shown in FIG. 6, aresuperposed onto the first and second axial end portions, respectively,of the laminated body 16 such that the chamfered portions 21 b faceoutward and the second recess portions 21 a are aligned with the slots16 a. The stator core 11 shown in FIG. 2 is prepared by applying severalstrips of laser welding (weld portions 18) on outer circumferentialsurfaces thereof so as to extend in an axial direction from the firstend portion to the second end portion. Moreover, the slots 16 a and thesecond recess portions 21 a line up in an axial direction to constitutethe slots 12.

[0043] As shown in FIG. 3, burrs 20 b extending in the press punchdirection remain on each layer of the first sheet 20 on inner wallsurfaces of the slots 12 of the stator core 11. A powdered form of anelectrically-insulating resin such as an epoxy resin, for example, iselectrostatically coated onto the stator core 11, then melted byheating, the electrically-insulating resin being formed so as to coverthe entire surface of the stator core 11.

[0044] In the stator 10 constructed in this manner, opening edgeportions of the slots 12 at the first and second end surfaces of thestator core 11 are constituted by the chamfered portions 21 b, and theburrs 20 b formed by press-punching are present only inside the slots12. Thus, damage to the electrically-insulating coating of the conductorwires 14 caused by the burrs 20 b is avoided during mounting of thestator winding 13 and during shaping of coil ends of the stator winding13, thereby improving electrical insulation.

[0045] Because end plates 17 having a thick sheet thickness are disposedon the first and second end portions of the stator core 11, the rigidityof the stator core 11 is increased. Thus, the occurrence of deformationand peeling of the first sheet 20 having a thin sheet thickness isprevented during insertion of the stator winding 13. When the stator 10is fixed by being held from first and second axial ends by a frame, theoccurrence of warping in outer circumferential portions of the statorcore 11 is reliably prevented. In addition, because the rigidity of thestator core 11 is increased, the sheet thickness of the first sheet 20constituting the laminated body 16 can be reduced. Thus, iron loss whichis proportional to the square of the sheet thickness of the steel sheetsis reduced, enabling increased efficiency to be achieved in thedynamoelectric machine.

[0046] Because the end plates 17 are prepared by joining together theabutted portions 21 c of the second sheets 21 by TIG welding, magneticflux can be passed through the end plates 17 effectively, enablingoutput to be stabilized.

[0047] Because the laminated body 16 constituting the stator core 11 isprepared by winding into a helical shape a single-strip first sheet 20formed by pressing a hoop material composed of the first magnetic steelsheet material, the first sheet 20 can be prepared from the firstmagnetic steel sheet material efficiently, enabling the amount ofmagnetic material used to be reduced, thereby enabling cost reductions.

[0048] Because the end plates 17 constituting the stator core 11 areprepared by bending into an annular shape second sheets 21 having apredetermined length formed by pressing a flat plate composed of thesecond magnetic steel sheet material, then TIG welding the first andsecond end surfaces of the bent second sheets 21 placed in contact witheach other, the second sheets 21 can be prepared from the secondmagnetic steel sheet material efficiently. In this case, five times asmany end plates 17 can be prepared as when the annular end plates arepress-formed directly from the second magnetic steel sheet material,significantly reducing the amount of magnetic material used, therebyenabling cost reductions. Furthermore, because the abutted portions 21 cof the second sheets 21 are joined together, handling of the end plates17 is facilitated when the end plates 17 are being superposed onto thelaminated body 16, improving manufacture.

[0049] When the chamfered portions are formed by chamfering annular endplates, as in the related art, the slot opening portions are narrow,making it hard to perform high-precision chamfering, thereby reducingyield. According to Embodiment 1, because the chamfered portions 21 bare formed on the edge portions of the second recess portions 21 a bychamfering the straight second sheets 21, the slot opening portions arewide, making high-precision chamfering possible, thereby enablingreliability to be increased.

[0050] Moreover, in Embodiment 1 above, the abutted portions 21 c of thesecond sheets 21 are joined together by TIG welding, but the abuttedportions 21 c of the second sheets 12 do not necessarily have to bejoined together; the first and second end surfaces of the second sheets21 constituting the abutted portions 21 c through which magnetic fluxflows need only be placed in contact with each other.

[0051] In Embodiment 1 above, the stator winding 13 is constructed bypreparing annular units by winding single conductor wires 14 eachcomposed of a copper wire coated with an electrical insulator for apredetermined number of winds, preparing star-shaped units by shapingthe annular units into a star shape, and mounting the star-shaped unitsinto the slots 12 of the stator core 11, but the stator winding is notlimited to this construction and it goes without saying that the statorwinding may also be constructed using the conductor segments 9 shown inthe conventional technique.

[0052] In Embodiment 1 above, insulators are not mounted to the slots12, but it goes without saying that insulators may be mounted to each ofthe slots 12.

[0053] Embodiment 2

[0054] In a stator core 11A according to Embodiment 2, as shown in FIG.7, the abutted portions 21 c of the second sheets 21 constituting theend plates 17 are aligned with one of several strip-shaped weld portions18 integrating the laminated body 16 and the end plates 17. In otherwords, the abutted portions 21 c are joined together simultaneously whenlaser welding is applied in order to integrate the laminated body 16 andthe end plates 17.

[0055] Moreover, the rest of this embodiment is constructed in a similarmanner to Embodiment 1 above.

[0056] A method for manufacturing the stator core 11A will now beexplained.

[0057] First, a single-strip first sheet 20 in which first recessportions 20 a are formed at a predetermined pitch is prepared bypress-forming a hoop material composed of a first magnetic steel sheetmaterial having a thickness of 0.35 mm, for example, using a press die.Then, the cylindrical laminated body 16 is prepared by winding the firstsheet 20 into a helical shape for a predetermined number of winds.

[0058] Second sheets 21 having a predetermined length in which secondrecess portions 21 a are formed at a predetermined pitch are eachprepared by press-forming a flat plate composed of a second magneticsteel sheet material having a thickness of 0.80 mm, for example, using apress die. Next, these second sheets 21 are faced using a press die toform chamfered portions 21 b on edge portions of the second recessportions 21 a on a first surface side of each of the second sheets 21.Then, the second sheets 21 formed with the chamfered portions 21 b areeach bent into an annular shape.

[0059] Next, the second sheets 21 which have been bent into an annularshape and in which the first and second end surfaces are abutted aresuperposed onto the first and second axial end portions, respectively,of the laminated body 16 such that the chamfered portions 21 b faceoutward and the second recess portions 21 a are aligned with the slots16 a. The stator core 11A shown in FIG. 7 is prepared by applyingseveral strips of laser welding (weld portions 18) on outercircumferential surfaces thereof so as to extend in an axial directionfrom the first end portion to the second end portion. Here, one of thestrips of laser welding is applied at the position of the abuttedportions 21 c of the second sheets 21. Thus, the second sheets 21 arejoined together at the abutted portions 21 c to form the end plates 17.

[0060] In addition, a powdered form of an electrically-insulating resinsuch as an epoxy resin, for example, is electrostatically coated ontothe stator core 11A, then melted by heating, the electrically-insulatingresin being formed so as to cover the entire surface of the stator core11A.

[0061] Consequently, similar effects to those in Embodiment 1 above canalso be achieved in Embodiment 2.

[0062] In Embodiment 2, because the abutted portions 21 c of the secondsheets 21 constituting the end plates 17 are joined togethersimultaneously when laser welding is applied to integrate the laminatedbody and the end plates, a single welding process is sufficient, therebysimplifying the manufacturing process.

[0063] Moreover, because the first and second end surfaces of the secondsheets 21 in the end plates 17 are placed in contact at the abuttedportions 21 c, the flow of the magnetic flux is not inhibited.Furthermore, in addition to the outer circumferential surface of thesecond sheets 21, the abutted portions 21 c may also be welded on theend surfaces on an opposite side from the laminated body 16 during laserwelding. In that case, magnetic flux can be passed through the endplates 17 effectively, enabling output to be stabilized.

What is claimed is:
 1. A method for manufacturing a stator core for adynamoelectric machine, said method comprising the steps of: preparing acylindrical laminated body by preparing a continuous first sheet inwhich first recess portions are formed at a predetermined spacing bypress-punching from a strip-shaped first magnetic steel sheet materialand winding said first sheet into a helical shape such that said firstrecess portions are superposed in an axial direction; preparing a secondsheet having a predetermined length in which second recess portions areformed at a predetermined spacing by press-punching a second magneticsteel sheet material having a sheet thickness greater than that of saidfirst magnetic steel sheet material; bending said second sheet into anannular shape; stacking said second sheets bent into the annular shapeon both axial ends of said laminated body such that said second recessportions are superposed on said first recess portions in an axialdirection; and integrating said laminated body and said second sheetsstacked together by applying several strips of welding on an outercircumferential surface of said laminated body and said second sheet soas to extend from a first end to a second end in an axial direction. 2.The method for manufacturing a stator core for a dynamoelectric machineaccording to claim 1, further comprising the step of joining togetherabutted portions of first and second end surfaces of said second sheetsbent into the annular shape before the step of stacking said secondsheets bent into the annular shape on said laminated body.
 3. The methodfor manufacturing a stator core for a dynamoelectric machine accordingto claim 1, wherein abutted portions of said second sheets bent into theannular shape are joined together simultaneously by said welding duringthe step of integrating said laminated body and said second sheets. 4.The method for manufacturing a stator core for a dynamoelectric machineaccording to claim 1, further comprising the step of forming anchamfered portion on an edge portion of said second recess portions bychamfering said second sheet before the step of bending said secondsheet into the annular shape.
 5. The method for manufacturing a statorcore for a dynamoelectric machine according to claim 4, furthercomprising the step of joining together abutted portions of first andsecond end surfaces of said second sheets bent into the annular shapebefore the step of stacking said second sheets bent into the annularshape on said laminated body.
 6. The method for manufacturing a statorcore for a dynamoelectric machine according to claim 4, wherein abuttedportions of said second sheets bent into the annular shape are joinedtogether simultaneously by said welding during the step of integratingsaid laminated body and said second sheets.